Radial sprues are common for low total production volume, low injection pressure molds. These molds are cheaper to build / machine, and use less expensive processing. Less conventional, though, which has hindered their acceptance for anything except niche applications. Like limited run model kits, for example...
Looks like it should build into a good model, although will probably require some work.
Last time I saw a Boomerang kit, it was the Airfix example, back in the mid to late 1960's.
I made a real mess of it, by accident, so tried to throw it away, but it came right back .................. yeah, I know !!!